During the processing of semiconductor wafers it is necessary to maintain proper orientation of the wafer during the many processing steps. Wafers are generally stored in wafer cassettes and are transported between processing stations in the cassettes. The cassettes are placed in the processing station and the wafers are removed by machine automated wafer handlers. The wafer handlers to not orient the wafers, but merely move them from the cassette to a processing station and back to the cassette. Therefore, it is necessary for the wafers to be properly aligned in the cassettes.
Some conventional wafer flat alignment apparatus have a wafer rotating drive roller with a diameter which is usually greater than one inch. The roller is covered with a sleeve made from polyurethane or silicone rubber. The alignment apparatus also has a vertical motion alignment plate and a vertical motion bearing plate, both of which are guided with linear guides. The plates generate micro particles as they move up and down. The drive roller surface tends to slip between the wafers and the roller surface, which motion tends to produce micro particles. Portions of the particles fall off the roller and become a source of wafer surface contamination. Particles remaining on the roller make the roller slippery. The area of the aligner beneath the wafers includes mechanisms that prevent the laminar flow of air to pass through the aligner. Particles that are generated during wafer rotation and alignment are blown upward, and some of the particles settle on the wafer surface causing defects. The micro particles are invisible to the eye and are a major clean room contaminator.